Summary of Pesticide Data from Streams and Wells in the Potomac River Basin
By Colleen A. Donnelly and Matthew J.Ferrari
Eighty-five water-soluble pesticides and pesticide degradation products were analyzed in 384 surface-water and Groundwater samples collected from the Potomac River Basin during March 1993 through September 1996. Thirty-nine of these compounds were detected in surface-water samples and 16 were detected in Groundwater samples. At least one pesticide was detected in 86 percent of the streams sampled and 45 percent of the wells sampled. Pesticides were detected more frequently and at higher concentrations in surface water than in Groundwater. The following four herbicides and one degradation product were the most frequently detected pesticides in both surface water and Groundwater: atrazine and metolachlor, which are used primarily on corn and soybean crops; prometon, which is used primarily in nonagricultural (urban and suburban) areas; simazine, which is used in both agricultural and nonagricultural areas, and desethylatrazine, which is one of the degradation products of atrazine. Insecticides were detected more frequently in surface water than in Groundwater. Diazinon, chlorpyrifos, and gamma-HCH (Undone) were found in more than 10 percent of surface-water samples, but in none of the Groundwater samples.